Positive mixing
Systems spontaneously and completely mix
Negative mixing
If not keep agitating, separate out
Neutral mixing
Hard to mix and hard to demix
Why is mixing important for drugs
Satisfactory mix ensures correct dose
What is a random mix
Probability of selecting particular type of particle is the same in all positions of the mix and equal to the proportion of such particles in the mix
What does the number of particles in scale of scrutiny depend on
Sample weight, particle size and particle density
What effect does number of particles have on variation
As number of particles increase, variation decreases
How to evaluate mix process
Use sample thief to take 10 samples from different depths and places to be representative of the mix
Disadvantages of a sample thief
Hard to push into powder, fine particles may lodge between tubes, particles may fracture
What is diffusion
Redistribution of particles by random movement relative to each other
What is convection
Movement of adjacent particle groups from one place to another
What is shear
Change in configuration of ingredients through formation of slip planes in mixture
What is powder segregation
Demixing, components separate out, can change mix from random to non random
Why does segregation arise
Powders mixed are usually not the same particle size, density or shape
How does particle size affect segregation
Smaller particles fall through the voids between larger, called percolation segregation
Trajectory segregation
During stirring larger particles have more kinetic energy and move greater distances
Elutriation segregation
Very small particles form dust which settles on top when mixing stops
How does density affect segregation
More dense particles tend to move down more
How does particle shape affect segregation
Spherical particles tend to have greatest flowability, and mix and segregate more easily
How are non segregating mixes affected by mixing time
Improve with increased mixing time
How are segregating mixes affected by mixing time
Have optimum mixing time, may start to demix with longer mixing
Ordered mix
Large particles and micronised particles, particles not independent of each other, there is a degree of order in mix
When can segregation occur in an ordered mix
Carrier particles vary in size, competition for active sites on carrier particle by other excipients, insufficient carrier particles cause excess small particles to separate out
What is the main mechanism of tumbling mixers
Diffusive mixing
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GIT Introduction17
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GIT Infections93
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IBS65
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IBD38
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Nutrition and dietary supplements66
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Oral and dental health33
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Hepatic disease55
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GORD38
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Peptic ulcer disease29
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Antiemetics45
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Sources of variability18
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Hepatic extraction ratio17
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Bioequivalance12
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Powders and granules32
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Particle size reduction + particle size distribution19
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Properties of powders33
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Mixing26
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Tablets81
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Oral solid dosage forms19
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Coating of tablets and multiparticulates33
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Solid oral MR dosage forms22
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Capsules23
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Rectal and vaginal solid dosage forms25
